“Cold Casting” is a term used to describe the process of mixing metal powder with a resin and applying the mixture into a mold. The finished casting can be made to have the appearance and weight of solid metal, if required. The metal cold cast process is faster and less expensive when compared with foundry casting of molten metal. Different metal powders such as aluminum, brass, nickel-silver, copper, and combinations thereof, can be used depending on the desired effect.
To make a metal cold cast composite product according to a prior art method, metal powder (typical mesh size 325 to 225) is mixed into a urethane resin until the mixture is thick and creamy. The mixture is then “slush-cast” (poured into a rubber mold and rolled around) or brushed onto the mold surface (gel coat) until the resin cures. The gel coat is then back-filled with straight resin, resin mixed with metal powder, resin mixed with lead shot (for weight), or a filler material. The entire mixture is cured until solid. To expedite the curing process, mild heat may be applied, such as by putting the filled mold into a curing oven.
To facilitate removal of the cured composite product, a release agent is sprayed over the entire mold surface prior to adding the liquid metal-resin mixture to the mold. Pigments may be added to the liquid metal-resin mixture prior to casting to achieve the desired colour.
Once curing is complete, the cast composite product is removed and lightly abraded with a medium/fine steel wool until the desired metal shine and luster are attained. The product may be finished with, for example, a base coat paint to give the casting added depth and dimension. To prevent oxidation of the metal, the finished casting may also be sprayed with a clear gloss spray (e.g. made of acrylic).
Traditional cold casting methods and products made thereby have a number of disadvantages.
One disadvantage is that each different final product must have its own mold. The mold is made using an original or prototype of the desired final product. This makes it more costly to manufacture products on a small scale. Once the production run is over, there is no longer a use for the mold and prototype or original. These articles tend not to be reusable and are often discarded and contribute to landfill.
Another disadvantage is that composite products made by traditional cold casting methods tend to lack tensile strength and not be very durable. They are prone to damage and breakage and do not resemble solid metal castings except in terms of their appearance and (sometimes) weight. Long curing resins can be used to reduce the amount of bubbles formed in the mixture by allowing time for the bubbles to rise to the surface and be released to the atmosphere. The fewer the bubbles, the greater the tensile strength of the finished product. However, the longer the curing time, the fewer products that can be made per unit time and therefore the higher the production costs. Moreover, even using long curing resins will not completely eliminate the appearance of bubbles in the final cured product.
The present invention is intended to at least partially overcome one or more of the above disadvantages by providing a relatively inexpensive, environmentally friendly method of cold casting that is suitable for the commercial production of custom “one-off” products as well as generic products on a large scale. Products made by the present method can be made denser, stronger and more durable than products made according to traditional cold casting methods, so as to more closely resemble articles made from foundry casting of molten metals.